stl_bvector.h (operator==(const _Bit_iterator_base&, const _Bit_iterator_base&)): Make hidden friend.

2019-05-11  François Dumont  <fdumont@gcc.gnu.org>

	* include/bits/stl_bvector.h
	(operator==(const _Bit_iterator_base&, const _Bit_iterator_base&)):
	Make hidden friend.
	(operator<(const _Bit_iterator_base&, const _Bit_iterator_base&)):
	Likewise.
	(operator!=(const _Bit_iterator_base&, const _Bit_iterator_base&)):
	Likewise.
	(operator>(const _Bit_iterator_base&, const _Bit_iterator_base&)):
	Likewise.
	(operator<=(const _Bit_iterator_base&, const _Bit_iterator_base&)):
	Likewise.
	(operator>=(const _Bit_iterator_base&, const _Bit_iterator_base&)):
	Likewise.
	(operator-(const _Bit_iterator_base&, const _Bit_iterator_base&)):
	Likewise.
	(_Bit_iterator::operator+(difference_type)): Likewise and allow NRVO
	copy elision.
	(_Bit_iterator::operator-(difference_type)): Likewise.
	(operator+(ptrdiff_t, const _Bit_iterator&)): Make hidden friend.
	(_Bit_const_iterator::operator+(difference_type)): Likewise and allow
	NRVO copy elision.
	(_Bit_const_iterator::operator-(difference_type)): Likewise.
	(operator+(ptrdiff_t, const _Bit_const_iterator&)): Make hidden friend.

From-SVN: r271096